1. Field of the Invention
The present invention relates to a motor driving device for rotationally driving a brushless motor.
2. Description of the Related Art
In brushless motors for household electric appliances such as fan motors for air-conditioners, a motor incorporating a motor driving device inside the motor is recently put into practical use. The motor driving device includes circuit components such as an inverter, a CPU (central processing unit), and a position sensor such as a hall element. In such a configuration, the CPU generates a switching signal to the inverter, and a motor winding is energized with a rectangular wave voltage or a sine wave voltage. Thus, the motor driving device drives the motor.
A host controller for controlling the motor driving device adjusts a duty command input to the motor driving device such that speed, air quantity or the like becomes a desired value, on a basis of a signal indicating the actual number of rotations, which is received from the side of the motor driving device, or the like.
FIG. 9 is a block diagram showing a configuration example of such conventional motor driving device 98. After AC power supply 11 is rectified by rectifier circuit 21 to be smoothed through smoothing capacitor 22, the DC voltage is supplied to three-phase inverter 23 included in motor driving device 98. Inverter 23 converts the DC voltage into an arbitrary AC voltage, and the converted AC voltage is supplied to motor 19. Position sensor 32 detects the position of a rotor of motor 19 to output this position as position detection signal Ps. Position detection signal Ps is supplied to position detector 34, the position of the rotor is computed to be supplied to FG output unit 54 as motor position signal Pd. FG output unit 54 outputs FG pulse signal FG indicating actual motor speed, on the basis of motor position signal Pd.
Additionally, FG pulse signal FG is supplied from FG output unit 54 to host speed controller 51 on the side of host controller 12. Host speed controller 51 adjusts duty command value D* such that speed, air quantity or the like becomes a desired value, based on FG pulse signal FG, to output adjusted duty command value D* to motor driving device 98.
Motor driving device 98 supplies, to voltage controller 57, duty command value D* received from host controller 12. Voltage controller 57 obtains values of three-phase voltage command values Vu*, Vv* and Vw*, from input duty command value D* and motor position signal Pd, to output the obtained values to PWM controller 59. PWM controller 59 generates a switching signal obtained by arranging pulses with duty according to the values of voltage command value Vu*, Vv* and Vw* in time series. Then, inverter 23 applies drive pulses Uo, Vo and Wo with duty according to this switching signal to the motor winding. By such operation, rectangular wave voltages or sine wave voltages are artificially generated from drive pulses Uo, Vo and Wo on the basis of pulse-width modulation (PWM), to be applied to the motor windings, thereby driving motor 19.
As a configuration example of such a motor driving device, for example, Unexamined Japanese Patent Publication No. 2001-292589 discloses a fan motor having a configuration in which an inverter is driven by drive pulses according to a duty command.
As a higher performance control system than rectangular wave drive system in which rectangular wave voltages are applies, or a sine wave drive system in which sine wave voltages are applied, described above, there is widely known a so-called vector control system in which a motor winding current is controlled in accordance with the position of a rotor. In vector control, a current in a magnet torque direction (q-axis current) that is generated by permanent magnets, and a current in a magnetic flux direction (d-axis current) that is generated by permanent magnets can be independently controlled. Therefore, it is possible to implement high efficiency, low noise, and high speed response, compared to the rectangular wave drive system or the sine wave drive system.
As a configuration example of a motor driving device using such a vector control system, for example, Unexamined Japanese Patent Publication No. 2004-40906 discloses a vector control device of a synchronous motor.
FIG. 10 is a block diagram of conventional motor driving device 99 that is configured to control motor speed by such vector control. Conventional motor driving device 99 shown in FIG. 10 also has a configuration in which motor 19 is driven by inverter 23. In FIG. 10, motor position signal Pd is supplied to differentiator 60. Differentiator 60 computes the speed of a rotor by differentiation of this motor position signal Pd. The speed thus computed is supplied to speed controller 56 as motor speed signal Sp indicating the actual speed of the rotor.
Speed controller 56 computes current command value I* from speed command value Sp* and motor speed signal Sp. Current controller 53 obtains three-phase voltage command values vu*, vv* and vw* from current command value I*, current detection signal Id indicating the winding current of a motor detected from current detector 31, and motor position signal Pd, to output three-phase voltage command values vu*, vv* and vw* to PWM controller 59. Herein, current controller 53 has a configuration based on the vector control system, and in current controller 53, a current is separated into a q-axis current in a torque direction and a d-axis current in a direction orthogonal to the torque direction for processing. Then, current controller 53 receives a current command for setting a current to current command value I*, and computes voltage command values vu*, vv* and vw* for supplying power to the motor windings.
Conventional motor driving device 99 shown in FIG. 10 attains high efficiency, low noise, and high speed response, as a configuration in which such a vector control system is used.
However, in a case where it is intended to introduce the vector control as it is, it is necessary to control by use of such a current command as to set the current to current command value I* like conventional motor driving device 99 shown in FIG. 10. Therefore, for example, in a case where the vector control is introduced to the configuration shown in FIG. 9, it is necessary to change a current command from the side of a host unit from a duty command to a current command, thereby causing a problem that not only a motor driving device but also a host controller are required to be changed.
In Unexamined International Patent Publication No. 2007/132889, when the vector control is introduced, an inverter circuit inside a motor is moved onto an external indoor control board, the generation of a switching signal that has performed by a CPU inside the motor is performed by a microcomputer on the indoor control board, which requires significant change.